Thousands of people immediately flooded online to share touching tributes, including numerous celebrities and friends of the actor.
And in particular, his Harry Potter co-stars have shared their own memories and messages about their loss.
Author J.K. Rowling led the tributes with this devastated tweet.
As well as this perfect feminist quote.
Rupert Grint released a statement, telling JustJared.com:
I am devastated to hear about the passing of Alan Rickman, I feel so privileged to have had the opportunity to work with him on numerous occasions – Even though he has gone – I will always hear his voice. My thoughts are with his friends and family at this time.
Michael Gambon, who played Albus Dumbledore in the franchise and worked on stage with Rickman, told BBC Radio 4:
Everybody loved Alan. He was always happy and fun and creative and very, very funny. He had a great voice, he spoke wonderfully well.
He was intelligent, he wrote plays, he directed a play. So he was a real man of the theatre and the stage, and that's how I think of Alan.